1. Field of the Invention
The present invention is related to a brushless dc motor having an ac control device. More particularly, the present invention is related to a brushless dc motor using a rectifier unit, a voltage-stabilizing control unit and a voltage-stabilizing unit to rectify and stabilize an ac power source.
2. Description of the Related Art
Referring to FIG. 1, U.S. Pat. No. 6,278,248, entitled “BRUSHLESS DC MOTOR FAN DRIVEN BY AN AC POWER SOURCE”, issued on Aug. 21, 2001 to HORNG et al, discloses a brushless dc motor fan. The brushless dc fan motor includes a converter circuit 1 consisted of a bridge rectifier 11, a resistor 12 and a filter 13. The converter circuit 1 employs the bridge rectifier 11 to convert an ac voltage into a dc voltage and to supply it to a motor drive circuit 2 and a sensor element 20. The resistor 12 is adapted to step down the dc voltage supplied from the rectifier 11 so that a step-down voltage is suitable for the use of the brushless dc motor. Consequently, the application of the brushless dc motor fan is suitable for ac power and may not be limited by a necessity of dc power.
The resistor 12 of the converter circuit 1 functions to step down an ac voltage so that the ac voltage is transformed into a low dc voltage that is suitable for a miniature brushless dc motor. For example, dc 110 V is transformed into dc 12 V or dc 220 V into dc 24 V. In this circumstance, the power consumption of the resistor 12 may result in a successive production of great heat. Thus, the brushless dc motor must be overheated in the normal operation when it is normally operated.
In addition, once the brushless motor is jammed, locked or failed, a rated current passed through the resistor 12 has a sudden increase that the power consumption of the resistor 12 may be increased. Consequently, the motor components including the resistor 12 may be destroyed if the power consumption is exceeded.
Referring to FIG. 2, U.S. Pat. No. 6,278,248 further discloses another converter circuit 1′ consisted of a capacitor set 14, a resistor set 15 and a zenor diode 16. The capacitor set 14 is a set of electrolytic capacitors adapted to filter power, and has a key feature of high Dissipation Factor (DF) that may result in a successive production of great heat. Similarly, the resistor set 15 may also result in a successive production of great heat.
The present invention intends to provide a brushless dc motor having an ac control device which includes a rectifier unit adapted to rectifier an ac power source. The ac control device further includes a voltage-stabilizing control unit and a voltage-stabilizing unit to thereby stabilize a dc power source converted from the ac power source in such a way to mitigate and overcome the above problem.